Dynamics and Mechanisms of the Multiphoton Gated Photochromic Reaction of Diarylethene Derivatives

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Dynamics and Mechanisms of the Multiphoton Gated
Photochromic Reaction of Diarylethene Derivatives

• Murakami, M. et al J. AM. CHEM. 2004, 126, 14764
• Miyasaka Lab
• Tomohiro Kunishi

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Contents

• Photochromism
• Motivation of the present paper
• Result Discussion
• Conclusion

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Photochromism
UV light
Vis. light
Photoinduced reversible transformation in a
chemical species between two forms without
changes of molecular weight.
Quick change of physical properties between two
isomers
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Motivation
Optical and Photonic Device
(5) Non-destructive read-out capability with the
high sensitivity needs another conditions arising
from the change of the some outer environments
that can act as gate of the reaction.
?Excited state reaction generally occurs in
competition with various processes in a finite
lifetime.
(3) Rapid response (4) high sensitivity
(2) low fatigue
Gated-Reaction Control via Multiphoton Laser
Pulse Excitation
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Photochromic Reaction
Open-form
Closed-form
lt 360 nm
450 700 nm
Reaction yield from closed-form to open-form is
only 1.3 under steady-state light irradiation.
Reaction yield????
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Transient absorption spectra of PT1(c) in
n-hexane excited with a 15-ps 532-nm laser
pulse.
Cycloreversion reaction completed within 100 ps.
Perfect recovery of the closed form by UV light
after ps 532 nm laser pulse.
Transient absorption????
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Time profile of trasient absorbance
lt femtosecond laser gt
lt picosecond laser gt
Time constant is almost the same.But, remaining
absorption is large.
10 ps decay / Reaction yield 1-2 . No
excitation wavelength effect.
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Apparent Reaction Yield
Drastic enhancement of the cycloreversion
reaction yield.1.3 (steady-state irradiation)
? 40 ( ps 532 nm laser excitation)
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Excitation intensity dependence conversion
efficiency at 160 ps after the excitation with a
15-ps 532-nm laser pulse.
Conversion efficiency is quadratically in
proportion with the exitation intensity
Conversion efficiency -DAbs590nm / Abs590nm
Slope2
Two-photon process is responsible for the
efficient bond breakage.
Conversion efficiency????
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Two-photon Absorption Processes
(1) Simultaneous two-photon absorption process
(2) Stepwise two-photon absorption process
Re-absorption of intermediate species The
competition of absorption of light between the
ground state molecule and the intermediate
species. ?Effective in the case where the number
of total photon is large.
Simultaneous two-photon absorption process
??????? Stepwise two-photon absorption process
???????
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Comparison of Picosecond and Femtosecond Lasers
Peak Energy Almost the same Total photon
number PS gt FS Peak Energy / Area
Size ( ) FS gt PS
However 1-2 (reaction yield FS)
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Two-photon Absorption Processes
(1) Simultaneous two-photon absorption process
(2) Stepwise two-photon absorption process
Re-absorption of intermediate species The
competition of absorption of light between the
ground state molecule and the intermediate
species. ?Effective in the case where the number
of total photon is large.
Simultaneous two-photon absorption process
??????? Stepwise two-photon absorption process
???????
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Excitation Intensity Dependence ( ps 532 nm laser
)
Increase in the S1 population with an increase in
the excitation intensity. Further increase of the
exc. Intensity decreases the S1 state population,
while increasing the So state bleaching.
S0
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Conclusion
Slope2
Gated-Reaction Control via Multiphoton Laser
Pulse Excitation
Total photon number
PS gt FS ? Stepwise
abosorption process PS gt FS
? Reaction
yield PS gt FS

• Optical memory

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Summary

• Picosecond pulsed excitation of the closed-isomer
  of the
• diarylethene derivatives led to the drastic
  enhancement of the
• cycloreversion reaction.
• this enhancement is attributable to the
  production of the higher
• excited state with a large reaction yield of the
  cycloreversion (50)
• Attained via a successive two-photon process.
• A new approach for one-color light control of the
  gated
• photochromic system, which can be utilized for an
  erasable
• memory system with nondestructive readout
  capability.